Method for making graphite whiskers

ABSTRACT

AN OVEN FOR MAKING WHISKERS FROM A VAPOR COMPRISING A HOUSING CONTAINING A CHILLED BASE PLATE, A FIRST AND SECOND SUPPORT POST EXTENDING UPWARDLY FROM THE BASE PLATE, AN UPPER AND LOWER SUPPORT PLATE MOUNTED ON THE POSTS, A HOLLOW HEATING ELEMENT MOUNTED BETWEEN THE SUPPORT PLATES, AND A STAGE WITHIN THE HEATING ELEMENT FOR SUPPORTING A SUBSTRATE ON WHICH WHISKERS ARE GROWN. THE SUBSTRATE IS COVERED WITH RHODIUM, AND MAY BE MADE OF A MATERIAL SELECTED FROM THE GROUP CONSISTING OF STAINLESS STEEL, BERYLLIUM OXIDE, ALUMINA, COPPER, COBALT, AND NICKEL. THE METHOD INCLUDES PLACING A SUBSTRATE IN A WHISKER DEPOSITION ZONE OF WHISKER VAPOR, AND DEPOSITING AND GROWING WHISKERS ON THE SUBSTRATE. THE METHOD ALSO INCLUDES COOLING THE BOTTOM OF THE WHISKER DEPOSITION ZONE TO FORM CONVECTION CURRENTS OF VAPOR PASSING UPWARDLY THROUGH THE ZONE, AND FEEDING THE VAPOR DOWNWARDLY INTO THE WHISKER DEPOSTION ZONE TO CLASH WITH THE UPWARDLY FLOWING VAPOR CONVECTION CURRENTS AND FORM A TURBULENCE IN THE WHISKER DEPOSITION ZONE. A ROTATABLE DRUM POSITIONED BELOW A NUCLEATING ZONE IN THE OVEN AND HAVING A POCKET THAT RECEIVES THE SUBSTRATE. A RACK GEAR OPERATED BY A MOTOR WITH A CLUTCH MOVES THE SUBSTRATE FROM THE NUCLEATING ZONE TO THE DRUM POCKET, AND A MOTOR GEAR SYSTEM ROTATES THE DRUM TO WIND THE WHISKERS IN THE FORM OR A ROVING ONTO THE DRUM SO THAT COURSES OF A SUCCEEDING LAYER OF ROVING LIE BETWEEN COURSES OF THE NEXT PRCEEDING LAYER HAVING COURSES RUNNING IN THE SAME DIRECTION.

y 23, 1972 E. F. HOLLANDER, JR 3,664,813

METHOD FOR MAKING GRAPHITE WHISKERS Filed July 17, 1969 4 Sheets-Sheet 14&0 X '177/ g%%%9u 7////LA ?Z///// I60 FIG, 5

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v T 70 F INVENTOR EDWARD R HOLLANDER,JL

QAfz 5A4 ATTORNEY May 23,

E. F. HOLLANDER, JR

METHOD FOR MAKING GRAPHITE WHISKERS 4 Sheets-Sheet 2 EDWARD F.HOLLANDER,Jr.-

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ATTORNEY y 1972 E, F. HOLLANDER, JR 3,664,813

METHOD FOR MAKING GRAPHITE WHISKERS Filed July L7. 1969 4 Sheets-Sheet 5INVENTOR EDWARD F. HOLLANDER, Jr.

ATTORNEY May 23, 1972 F. HOLLANDER, JR 3,664,813

METHOD FOR MAKING GRAPHITE WHISKERS 4 Sheets-Sheet 4 Filed July 1.7,1969 FIG. 7.

INVENTOR. EDWARD F. HOLLANDER, Jr.

ATTORNE Patented May 23, 1972 Filed July 17, 1969, Ser. No. 842,560 Int.Cl. C01b 31/04, 31/07 US. Cl. 213-2091 9 Claims ABSTRACT OF THEDISCLOSURE An oven for making whiskers from a vapor comprising a housingcontaining a chilled base plate, a first and second support postextending upwardly from the base plate, an upper and lower support platemounted on the posts, a hollow heating element mounted between thesupport plates, and a stage within the heating element for supporting asubstrate on which whiskers are grown. The substrate is covered withrhodium, and may be made of a material selected from the groupconsisting of sta nless steel, beryllium oxide, alumina, copper, cobalt,and mckel. The method includes placing a substrate in a whiskerdeposition zone of whisker vapor, and depositing and growing whiskers onthe substrate. The method also includes cooling the bottom of thewhisker deposition zone to form convection currents of vapor passingupwardly through the zone, and feeding the vapor downwardly into thewhisker deposition zone to clash with the upwardly flowing vaporconvection currents and form a turbulence in the whisker depositionzone. A rotatable drum positioned below a nucleating zone in the ovenand having a pocket that receives the substrate. A rack gear operated bya motor with a clutch moves the substrate from the nucleating zone tothe drum pocket, and a motor gear system rotates the drum to wind thewhiskers in the form of a roving onto the drum so that courses of asucceeding layer of roving lie between courses of the next preceedinglayer having courses running in the same direction.

BACKGROUND OF THE INVENTION This invention relates to a method and anoven for making fibers or whiskers by condensing material from a vaporphase, and a drum for winding the whiskers into a coil in the form of aroving.

It has long been known that crystal structures are very much strongerthan the same material in non-crystalline form. Accordingly, it has beendesired to produce crystalline material having long, needle-like linearcrystals, commonly referred to in the art as crystalline fibers orwhiskers. Much work is being done to develop a reliable method andapparatus for producing whiskers, such as graphite whiskers.

SUMMARY OF THE INVENTION It is an object of this invention to provide amethod and apparatus for producing whiskers reliably and consistently,and for winding the whiskers into a coil. This involves providing anoven including a chilled base plate and a hollow heating element mountedabove the base plate with a stage positioned within the heating elementfor supporting a substrate on which the whiskers are grown. Thesubstrate may be made of a number of materials, and it has been foundthat when the substrate is covered with rhodium that whiskers areproduced at a greatly accelerated rate. Also, it has been foundbeneficial to create convection currents of vapor in the oven which flowupwardly through the heating element, and to direct the feed vapordownwardly through the heating element to form a turbulent depositionzone within the heating element. It also involves providing a drum andmeans for winding the whiskers on the drum in the form of a roving.

BRIEF DESCRIPTION OF THE DRAWINGS Other objects and advantages of thisinvention, including its simplicity and economy, as well as the easewith which it may be adapted to existing equipment, will further becomeapparent hereinafter and in the drawings, in which:

FIG. 1 is a view, partly schematic, of whisker oven apparatusconstructed in accordance with this invention;

FIG. 2 is view in vertical section of the oven of FIG. 1;

FIG. 3 is a perspective and exploded view of an outer heat shieldhousing forming part of the oven;

FIG. 4 is a view partly in section of the winding apparatus of thisinvention;

FIG. 5 is a view in section taken as indicated by the lines and arrows5-5 which appear in FIG. 4;

FIG. 6 is a view in section taken as indicated by the lines and arrows6-6 which appear in FIG. 4; and

FIG. 7 is an exploded view in schematic form of feed structure locatedbetween nucleation zone and the drum of the winding apparatus.

Although specific terms are used in the following description forclarity, these terms are intended to refer only to the structure shownin the drawings, and are not intended to define or limit the scope ofthe invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT Turning now to the specificembodiment of the invention selected for illustration in the drawings,there is shown a whisker oven 11 comprising a housing 13, an outerheat-shield 14, an inner heat-shield 15 containing a chilled base plate16, a first support post 17 and a second support post 19 extendingupwardly from base plate 16, an upper annular support plate 21 and alower annular support plate 23 mounted on posts 17 and 1'9, a hollowgraphite heating element 25 mounted between support plates 21 and 23,and a chilled stage 27 mounted within heating element 25 for supportinga substrate 29 on which whiskers 31 are grown.

Oven 11 includes electrical insulators 33 positioned between the posts17, 19 and base plate 16. An electrical insulator 35 is positionedbetween support post 19 and upper support plate 21, and electricalinsulator 37 is positioned between support post 17 and lower supportplate 23. A source of electric current 39 is connected by electricalconductors 41 to support posts 17, 19, so that current flows throughpost 19, lower support plate 23, heating element 25, upper support plate21, and downwardly through support post 17 to return to current source39 to thereby heat the heating element 25.

Three molybdenum discs 4345 are supported from posts 17, 19 by rods 47and ring 48 and are positioned below heating element 25 to preventexcessive heat loss downwardly.

Above heating element 25, a molybdenum disc 49 is supported from posts17, 19 by annular plate 51 and forms a heat shield for preventingexcessive heat loss upwardly. Electrical insulators 53 are positionedbetween plate 51 and posts 17, 19 to prevent electrical curren flow fromposts 17, 19 to plate 51. e

A hollow cylinder 5-5 of fused quartz is supported between plates 21 and23 and is positioned around heating element 25 for preventing excessiveheat loss outwardly.

A gas or vapor, such as methane or natural gas, is fed into oven 11 froma vapor source through a tube 59 encased in a stainless steel sleeve 61threaded into base plate 16 and having a plastic insert 63 positionedbetween tube 59 and sleeve 61 to electrically insulate the 3 tube 59from base plate 16. Insert 63 is preferably made of Teflon, and a tubeclamp 65 is provided for adjusting the vertical position of tube 59,since normally clamp 65 abuts the top of insert 63.

Apparatus is provided for varying the pressure in oven 11, and thisapparatus includes a tank 67 (FIG. 1) comnected to oven 11 by conduit69, flowmeter 70, valve 71, and tube 59. Argon and methane, or hydrogenand methane are mixed together in a mixing vessel or tank 67 which issimilar in construction to oven 11, and the mixture of gases is fed intothe interior of oven 11 until the desired pressure is reached.Satisfactory results in growing whiskers have been obtained at oneatmosphere, but operation at about 4 or 5 atmospheres is preferred. Inany event, the pressure within oven 11 must be positive, since nodeposition of whiskers has been obtained at negative pressures.

Vacuum line 74, sufficient to exhaust the furnace to -4 torr, isprovided for scavenging undesired vapors and gases, such as oxygen, fromthe furnace before beginning nucleation and growth of the crystalwhiskers. Exhaust line 76 is provided for controlling the pressure inthe furnace and for exhausting the unwanted decomposition products ofthe reaction, such as hydrogen in the case of methane.

While whisker deposition has been obtained using substrates made of avariety of materials, it has been found that when the substrate is madeof some other materials there is no whisker deposition. For example,whisker deposition has been obtained when the substrate has been made of300 series stainless steel without selenium or sulfur or similar agentsused for free machining, beryllium oxide, alumina, copper, cobalt andnickel. Moreover, greatly accelerated graphite whisker deposition wasobtained when the substrate was coated with rhodium. The rhodium appearsto act as a catalyst and produces a fibrous, woolly, cotton-ballmaterial which may be used to reinforce rubber, for example. The use ofrhodium increased the nucleation and growth of the whiskers about tenthousand times.

Not all materials may be used as a substrate. For example, tests haveshown that the following materials do not work as a substrate to producegraphite whisker deposition and growth: silica, aluminum, tungsten,molybdenum, gold, and silver.

The temperature of heating element 25 may be varied by varying theoutput of the electrical current source 39. For graphite whiskernucleation and growth to occur at all, a specific thermal gradient isimportant and also the absolute temperature of the substrate isimportant. Moreover, the temperature must stay fixed and not wander. Forexample, the substrate temperature may be 1150 'F. or 1250 F., butwhichever temperature is chosen, the substrate should stay within about1 F. of that chosen temperature.

Gas tube 59 extends upwardly and then curves downwardly to feed the gasdownwardly into a whisker nucleating or deposition zone 72 aroundsubstrate 29 and form a turbulence with vapor convection currentscreated by the coolness of chilled base plate 16.

Base plate is cooled by a cooling tube 73 and outer heat shield 14 iscooled by cooling tubes 75.

Heating element 25 is supported on plate 23 by split ring clamps 77 andbolts 79, and stage 27 is supported by rods 81 that extend upwardly fromdisc 43.

An annular molybdenum disc 83 is positioned within heating element 25above stage 27 and is supported by rods 85 that extend downwardly frommolybdenum disc 49.

Fused quartz cylinder 55 is held reasonably concentric to heatingelement 25 by a shoulder 87 on clamping ring 77.

Inner heat-shield is preferably made of molybdenum, and is provided withan annular cover 89 having 4 a hole 91 through which tube 59 projectsdownwardly toward nucleating zone 72.

Electrical conductors 95, 96 pass through the bottom of housing 13 andlead,'respectively, to thermocouple 97 bolted to the bottom of stage 27and to thermocouple 99 positioned between heating element 25 and quartzcylinder 55'.

Whisker oven housing 13 is a split tank and is provided with vacuum andpressure gauges, side windows 101 for looking into the interior, and alarger window 103 at the top.

Outer heat-shield 14 is provided with a top wall 105 having three sightholes 106-108 of various sizes and a bearing 109 on which a top plate111 is rotatable. Plate 111 has a sight hole 113 that may be positionedover any of sight holes 106-108 as desired so as to watch the nucleationin zone 72.

Substrate 29 is cylindrical in shape and the whiskers 31 grow on theouter surface of the cylinder. However substrates of different shapesmay be used.

In practice, it has been noted that if there are too many vapor atoms inthe oven trying to deposit on the substrate 29, proper nucleation doesnot occur. On the other hand, I have achieved nucleation, followingcareful purging of the oven by pumping the vacuum chamber to aboutmicron, refilling the chamber with a clean inert gas such as argon andrepeating these steps three times until the level of contamination islow, by setting the proper thermal gradient in the oven by heating theelement 25 to about 1450 F. with the pressure in the oven 11 being anegative pressure, i.e. a vacuum. Then I flooded the oven 11 withnatural gas containing methane until the pressure rose above fifteenmillimeters of mercury to start deposition of whiskers. Then I droppedthe temperature of the heating element 25 to about 1200 F. and thegrowth of whiskers continued.

Chilled base plate 16 serves a dual purpose in that it protects theinstruments below plate 16 from heat, and also promotes convection ofvapor current in the oven to thereby stimulate and promote the growth ofwhiskers.

A temperature gradient exists between heating element 25 and substrate29. Similarly, a tempearture gradient exists between heating element 25and the whisker growth ends 31. Satisfactory growth has been achievedwhen these gradients were between 300 F. per inch and 1200 F. per inch.This is a function of the geometry of the furnace.

The method of the present invention comprises placing a substrate 29 ina whisker deposition zone 72 of whisker vapor by placing substrate 29 onstage 27, and depositing and growing whiskers on the substrate 27. Thesubstrate is made of a material selected from the group consisting ofrhodium, stainless steel, beryllium oxide, alumina, copper, cobalt andnickel, and excellent results have been obtained from a beryllium oxidesubstrate coated with rhodium. Graphite whiskers have been grown usingmethane as the vapor, and also when using neutral gas containing a highpercentage of methane.

The temperature of the whisker vapor has been maintained in thedeposition zone at about 1200 F., and whisker deposition has beenobtained with the pressure at fifteen millimeters of mercury, oneatmosphere, and up. However, no whiskers were obtained when the pressurein the oven has been negative.

The method also includes the steps of cooling the bottom of the whiskerdeposition zone by chilling plate 16 to form convection currents ofvapor that pass upwardly through the vapor deposition zone, and feedingthe vapor downwardly from tube 59 into the whisker deposition zone toclash with the upwardly flowing vapor convection currents and form aturbulence in the vapor deposition zone around the substrate 29.

Referring now more particularly to FIGS. 3-7, there is shown windingapparatus which may be incorporated in the whisker oven and positionedbelow a nucleating zone 72a that corresponds to nucleating zone 72 inFIG. 2. A base plate 16a corresponds to base plate 16 in FIG. 2. Most ofthe apparatus in FIG. 2, is duplicated in FIG. but has been omitted forclarity. However, some of the structure of FIG. 2, the supportingstructure lying between the nucleating zone 72 and base plate 16, isleft out entirely because substrate 29a is adapted for movementdownwardly from nucleating zone 72a through a hole 115 in plate 16a toseat in a pocket 117 formed in a drum 119 rotatable in the direction ofarrow 121.

The winding apparatus includes drum 119 having a gear 123 that rotatedby an elongated gear 125 mounted on a shaft 127. A left-hand helicalgear 129 is also mounted on shaft 127 and is caused to rotate when shaft127 moves around a fixed left-hand helical gear 131 supported in fixedposition by stationary shaft 133 that extends upwardly from fixed plate135.

Shaft 127 is caused to move around fixed gear 131 by the rotation ofgear 137 on which is mounted end plates 139, 141. Shaft 127 is mountedsupported at its ends in plates 139, 141. A third end plate 143 connectsone end of plate 139 to an end of plate 141 to form a strong threesidedbox structure of plates 139, 141 and 143.

Gear 137 is caused to rotate by a pinion 145 mounted on the shaft ofmotor 147.

Drum shaft 149 is mounted between end plates 139 and 141 and ispositioned interiorly of drum 119. A gear 151 is mounted on the end ofshaft 149 and is driven by a pinion 153 of shaft 127. Pinion 153 has aslightly larger pitch diameter than elongated gear or pinion 125. Shaft149 is provided with a cam groove 155, and drum 119 is provided with ahole 157 in which is positioned a springloaded stern 159 having a shoe161 that rides in groove 155 to give axial movement to drum 119. Theteeth of pinion 153 have a slightly larger pitch diameter than the teethof pinion 125 so that the speed of the axial movement of drum 119 isslightly different than that dictated by revolutions of pinion 125 andgear 123 alone. Accordingly, courses of a succeeding layer of roving liebetween courses of the next preceeding layer having courses running inthe same direction.

A support plate 163 is provided for supporting a bearing 165, and abearing 167 is mounted in gear 137. Bearings 165 and 167 serve asbearings about which the entire frame assembly including gear 137 andend plates 139, 141 and 143 rotate. A hearing 169 supports gear 131, anda bearing 171 and support sleeve 173 support helical gear 129.

To raise and lower substrate 29a, a gear rack 175 is provided having areduced end portion 177 which is received by a hole in the bottom ofsubstrate 29a. Gear rack 175 is driven by a driving gear 179 mounted onshaft 181 of motor 183 having an electrically operated clutch on itsshaft 181. When rack gear 175 is moved downwardly to deposit substrate29a in pocket 117, switch 185 is activated to open the clutch on motor183 thereby allowing rack gear 175 to drop quickly by gravity to aposition clear of drum 119 as shown in FIG. 4. This use of theclutch-motor is advantageous over using a complicated and expensive twospeed motor.

FIG. 7 is an exploded view in schematic form of the feed structure ofthe invention located between nucleating zone 29a and chilled base plate16a. A ring 187, preferably of alumina, forms a funnel guide forwhiskers 31 to aid in restricting the movement of the whiskers outsidenucleating zone 29a. A pair of forks 189, shown separated, are broughttogether by a solenoid acting upon a signal from switch 185. The forks189 hold the whiskers 31 as they pass through the forks and prevent thegrowth ends from turning as the roving is twisted below. A pair of splitguides 191 are also brought together by a solenoid upon a signal fromswitch 185 and in closed position, the guides 191 form a circular orcylindrical hole through 6 which whiskers 31 pass and are supported inan upright position. Guides 191 support the weight of the long rovingand add some tension to the roving as it winds onto the drum 119.

A pair of tension rolls 193 are positioned beneath guides 191 and arespring loaded by spring 195. Rolls 193 are brought together by asolenoid that is actuated by switch 185 and they apply tension to theroving to aid in the winding of the roving onto drum 119. Rolls 193 andguides 191 are preferably made of alumina, and forks 189 are preferablymade of 310 stainless steel.

Drum 119 is provided with a self-supporting cone 197 which is shown insection in FIG. 4 and which slips on and off drum 119 to form the coreof the round roving. To mount cone 197 on drum 119, the operator pullsout shaft 149 from its hearings in end plates 139 and 141, and then cone197 is slipped over drum 119. To remove cone 197 from drum 119 when thecone has been wound with whiskers, the reverse procedure is followed:shaft 149 is pulled out of its bearings and the cone 197 is pulled offdrum 119.

In operation of the winding apparatus shown in FIGS. 3 to 7, substrate29a is moved upwardly into nucleating zone 72a by rack gear 175 andnucleation is started. As nucleation progresses and the whiskers 31grow, substrate 29a is moved downwardly by rack gear 175 at such a speedthat the wisps of the whiskers 31, the growing ends, remain innucleating zone 72a. When the substrate 29a seats in pocket 117 of drum119, switch 185 actuates the clutch mechanism of motor 183 to releaseits clutch mechanism so that rack gear 175 drops very quickly by gravitythrough the hole in drum 119 to the position shown free of the drum inFIG. 4. Then motor 147 starts to rotate pinion which rotates the entireassembly mounted on gear 137 including end plates 139, 141 and shafts127 and 149. The rotation of shaft 127 in a horizontal plane parallel tothe plane of gear 137 causes rotation of shaft 127 as helical gear 129moves around fixed helical gear 131. Rotation of shaft 127 causesrotation of pinion 125 which rotates gear 123 and drum 119. Rotation ofshaft 127 also causes rotation of pinion 147 which rotates gear 151 anddrum shaft 149 at a different rate of speed from the rotation of gear123 and drum 119.

With drum 119 rotating, the whisker roving is wound on drum 119 as theaction of shoe 161 in groove 1S5 moves drum 119 back and forthlongitudinally. Because pinion 153 rotates gear 151 at a different speedthan that which pinion rotates gear 123, the courses of a succeedinglayer of roving lie between the courses of the next preceding layerhaving courses running in the same direction.

The feed of the roving into the drum is controlled by ring 187, forks189, guides 191 and tension rolls 193 positioned above the drum.

When the roving has been fully wound on drum 119, the winding is removedby removing cone 197 from the drum in the manner herein beforedescribed. Then the cone is removed from the interior of the coil, andthe strand of whiskers may be unwound from the coil by pulling from theinside or interior of the coil.

The entire apparatus may be used vertically inverted, and the resettingof the mechanism is simplified by using motors with clutches in theiroutput shafts. The twist in the roving is preferably in the order of onetwist per three inch length of roving, and the pull rate of the rovingis preferably about four inches per hour or faster.

What is claimed is:

1. In a method of making graphite whiskers by depositing and growingwhiskers on a substrate, the steps comprising covering the substratewith rhodium, placing the rhodium covered substrate in a whiskerdeposition zone of hydrocarbon whisker vapor, maintaining said zone atpositive pressure at about 1150-1450 F., providing a temperaturegradient around said substrate by chilling said substrate and depositingand growing whiskers on the rhodium covered substrate.

2. In a method of making graphite whiskers by depositing and growingwhiskers on a substrate, the steps comprising providing a substrate madeof a material selected from the group consisting of rhodium, 300 seriesstainless steel, beryllium oxide, alumina, copper, cobalt, and nickel,placing the substrate in a whisker deposition zone of hydrocarbonwhisker vapor, maintaining said zone at about 1150-1450" F., providing atemperature gradient around said substrate by chilling said substrate,and depositing growing whiskers on the substrate.

3. The method of claim 2, including holding the temperature of thesubstrate in the deposition zone steady at a desired temperature.

4. The method of claim 2, wherein the whisker vapor is methane.

5. The method of claim 2, wherein the whisker vapor is natural gas.

6. The method of claim 2, wherein the whisker vapor is an aromatichydrocarbon.

7. The method of claim 2, wherein the pressure in the whisker depositionzone is in the range of about 1-5 atmospheres.

References Cited UNITED STATES PATENTS 2,796,331 6/1957 Kautfman et al.23209.4 3,107,180 10/1963 Diefendorf 117226 3,246,950 4/1966 Gruber23208 3,378,345 4/1968 Bourdeau et a1. 23209.1

FOREIGN PATENTS 998,166 7/1965 Great Britain 23-.208

0 EDWARD J. MEROS, Primary Examiner U.S. Cl. X.R. 23--209.5, 273

